A typical well has a metal lining called a casing that extends throughout several subsurface formation strata; each formation may contain different fluids such as water, gas, oil or a mixture thereof. The aim of the casing is to isolate the different formations and their fluids. To produce only the desired effluents, the casing is perforated at the depth the formation contains the desired fluids and the other zones are left unperforated to prevent unwanted fluids at other depths from flowing into the casing. The effluents are removed from the well through the use of a second pipe lowered inside the casing called production tubing by either the inherent pressure of the fluid in the formation or by the use of artificial lift mechanisms if the formation pressure is not sufficient to lift the well's effluents on its own. Typically the produced effluents are a mix of fluids such as oil, gas and water. Depending on the percentage of each type of effluent, the well will perform as expected or not. A high water production might produce sufficient hydrostatic pressure in the wellbore to counteract the formation pressure and therefore not allow the effluents to reach the surface on its own. A production facility may not be equipped to handle high production rates of gas. Most wells, at a given point of their life need to be evaluated to correct problems with the well's equipment, low production or excess of unwanted effluents.
To evaluate hydrocarbon or water well production, the industry regularly relies on what are commonly known as logging tools. Depending on the information required, these logging tools might also be called production logging tools. Such tools have packaged sensors to characterize formation and fluid properties. The logging tools are typically lowered into the wellbore via a cable through the well's production tubing. Alternatively the production logging tools can be lowered via slick line (a cable with no conductors), coiled tubing, production tubing or similar means. The reason for using production logging tools in a well are varied and common throughout the life of a well: to investigate water entry, a reduction of production rates, gas entry, paraffin production, casing collapse, commingled production, thief zones, bad cementing, perforating efficiency and many others. The use of production logging tools is the cheapest, widest used and most convenient way to evaluate possible current or future problems in the life of a producing well but there is one condition needed: the well has to be flowing at a minimum volume of effluents in order to evaluate it.
Typically wells logged with these production logging tools are capable of flowing by themselves by initially lowering the hydrostatic column but inevitably the producing formation will deplete as hydrocarbon, gas or water is produced so the pressure from the formation will eventually not be enough to push the effluents to the surface without help. Increasingly a vast number of producing wells are depleting to the point the hydrocarbon needs to be extracted by other means generally called artificial lift mechanisms. Such artificial lift mechanisms include gas lift, electrical submersible pumps (ESPs), downhole pumps, swabbing, “pumping jacks” and numerous other mechanisms which a person skilled in the art will have no problem recognizing. Some estimates widely used in the industry indicates 70% of the world's producing oil fields are in a depletion stage known as “brown fields” needing one or another artificial lift mechanism to produce as the formation pressure is insufficient to lift the effluents to surface at economical rates.
One of the preferred methods for artificially lifting effluents to the surface in these depleted or low rate producing wells is to use a downhole pump. These pumps are generally electrically driven by lowering a power cable from surface to the pump located at the lower end of the production tubing. The design of such pumps do not allow any logging tools to go through it and therefore making it impossible to evaluate the well without retrieving the downhole pump. With the downhole pump in place, the well may produce at the rate required to collect meaningful production logging information but there is not a physical path to lower the production logging tools to the producing formation in order to evaluate it. On the other hand if the downhole pump is retrieved from downhole to allow the production tools to reach the formation needing to be evaluated, then the lack of a downhole pump prevents the producing well from producing the minimum production of effluents needed to evaluate it.
The industry has tried for a long time to find ways to characterize the formation and produced fluids from this type of depleted wells. One such attempt is described in U.S. Pat. No. 5,186,048 dated Feb. 16, 1993, entitled “Method and apparatus for logging a well below a downhole pump” issued to Brian Foster et al., where the inventors propose the use of a production logging tool below a downhole pump with all the equipment needed lowered via production tubing. The method described in the above mentioned patent requires the production logging tools to be lowered into the wellbore to a predetermined depth, then the wireline cable used for lowering and communicating with the production logging tools is cut and fed through a series of adapters designed to pass the wireline cable from the outside of the production tubing to the inside of the production tubing; as each of the joints of production tubing are lowered into the borehole the wireline cable is attached at surface to support the production logging tool, the production logging tool remains at the same depth as the joints of production tubing are lowered one by one; the cable is disconnected every time a new joint is fed at surface, the surface side of the cable is then passed through the new production tubing joint and re-attached to the downhole end of the wireline cable; once the bottom of the production tubing reaches the production logging tool, the tools is “housed” in a protecting sleeve while the well head equipment (blowout preventor, pressure gear, etc.) is rigged up at the surface to be able to flow the well safely. After the safety equipment is rigged up, the downhole pump is started so the well starts producing and the production logging tools are freed from the protective sleeve; the production logging tools is now free to go up and down recording the required data to characterize the formation and effluents.
A proposed alternate solution to logging wells that will not flow on its own is described in United Kingdom Patent Application No. GB2383357 filed on Dec. 17, 2002, entitled “A system and method for logging and modifying the flow of downhole fluids” by Peter Schrenkel et al. wherein an artificial lift mechanism is lowered into the wellbore together with a production logging tool and a retrievable fluid barrier. These components are lowered at the same time with the production logging tool “housed” inside a protective sleeve. The aim is to plug a segment of the wellbore, characterize the formation and effluents for that perforated interval and then retrieve the fluid barrier. The wireline cable is passed from the inside of the protective sleeve to the outside and the wireline cable and the means used to lower the inventive apparatus are lowered into the wellbore at the same time. Once the retrievable fluid barrier is set in place, the production logging tool is free to move up or down in order to characterize the formation and effluents. Once the required information is collected the production logging tool is returned to the protective sleeve and the retrievable fluid barrier is retrieved to be repositioned and the process started again as needed.
It is an object of the present application to provide an improved apparatus and method for characterizing well effluents and a method for treating a well that avoids one or more of the problems with prior art apparatus and methods and/or provides one or more benefits over prior art apparatus and methods.